This invention relates generally to the high-speed inspection of any tape product where errors are sensed and returned to an inspection or correction station before proceeding with the inspection.
More particularly the invention relates to improved process and apparatus for inspecting magnetic recording tape, particularly digital (computer) tape.
The following description of the prior art is necessarily made with hindsight of the invention described for the first time in the Specification appearing below. Therefore, it is to be understood that the insights into the limitations of the prior art described herein are not to be taken to be part of the prior art as it was known prior to the present invention.
Magnetic tape, especially digital magnetic tape of the type used in computer memory applications, is a well-known product of commerce. Such tape is used in maintenance of critical business records. Any defect in the tape may cause serious problems for the company which is relying upon the accuracy of the information which has been magnetically recorded on the tape. Consequently, such computer tape is always inspected to assure its compliance with the required high standards of quality. Indeed, much of the computer tape sold is certified by the supplier to be error free.
The inspection of computer tape is normally carried out at high speed, e.g. 200 inches per second or higher. Typically, the tape is cleaned under a scraper blade and then passed under a read/write head. "Test Data" is written magnetically on the tape by a write head and, immediately, the data is read by a read head. The read head is used to confirm that the test data can be both written upon and recovered from the magnetic tape. When the data to have been written is not present, the read head has detected an error, and the error-bearing situs of the tape must be returned to an "inspection station" or to a station at which the tape is subjected to some remedial steps. The remedial steps may include another or different automatic scraping in an attempt to remove the defect mechanically or they may include the manual removal of a defect by a skilled person who views the defect under a microscope. In any event, but in particularly in the latter situation, it is desirable that the defect in the tape be placed precisely at the desired position, e.g. directly under the microscope.
In the past, the movement of the tape has been achieved by timing the required movement. By this is meant that the apparatus would move the tape segment bearing the error into the inspection station by moving it for a time which would, theoretically, position it precisely at the desired location. However, very frequently the tape would fall outside the area in which a worker could view the tape. This was particularly true if movement under the station followed a plurality of attempts to remove the defect under a mechanical scraping station. The site of the error would simply become "lost" and it would be time consuming for a worker to find it. Attempts to avoid this problem have been met with limited success. Attention to mechanical problems, such as slippage of the tape or gears associated with the apparatus has not solved the problem.
The error-bearing portion of the tape might be out of position by a significantly large fraction of an inch, i.e. 0.5 of an inch, or even one inch. Generally, operators would rather move the tape error into the inspection position by hand than rely upon the time-consuming recall procedure.
A Control Data Corporation Model 686 tape certifying apparatus is typical of the prior art inspection devices.